Nicodemo “Little Nicky” Scarfo, the boss of the Philadelphia-South Jersey La Cosa Nostra crime family in the 1980s, has been described by law enforcement officers and former criminal associates as ruthless, homicidal, greedy and paranoid — even by organized-crime standards.

Today, Scarfo, 83, sits in federal prison in large part because of Philip “Crazy Phil” Leonetti, his close nephew and criminal underboss, who became a witness against him.

In “Mafia Prince,” Leonetti tells the inside story of his uncle’s rise to the leadership of the crime family and his violent seven-year reign. Leonetti also writes about his own criminal acts, which include 10 murders.

Leonetti tells of being born into La Cosa Nostra. In the absence of Leonetti’s father, Scarfo became a surrogate father, raising Leonetti from childhood in their way of life.

Leonetti committed his first murder when he was 23, and he went on to commit countless other murders and criminal acts at his uncle’s side. Between 1976 and 1987, Scarfo and Leonetti made millions of dollars through illegal gambling, loan sharking, extortion and skimming from the Atlantic City casinos.

The two were feared and respected by those in the underworld. A radio DJ called Leonetti “Crazy Phil,” and the nickname stuck. Leonetti said he hated the moniker, but his uncle said most mob guys would love to have a nickname like that.

In “Mafia Prince” Leonetti offers a history of the Philadelphia mob, including the murder of longtime mob boss Angelo Bruno in 1980 and how Scarfo became the boss after Bruno’s successor, Philip “Chicken Man” Testa, was murdered a year later by a powerful nail bomb on his front porch in South Philly.

Scarfo became the boss in 1981 and began an internecine mob war, leaving bodies on the streets of South Philly. He shook down drug dealers and gamblers and beat or murdered anyone who did not show him the proper “respect.”

Leonetti also writes about accompanying his uncle to meetings with notorious gangsters including Meyer Lansky in Miami and John Gotti and Sammy “the Bull” Gravano in New York.

When Scarfo and Leonetti finally were convicted and received long sentences in prison, Leonetti made a deal with the feds and testified against his uncle and other organized-crime figures.

Being half-Italian and raised in South Philadelphia — the hub of the Philadelphia-South Jersey La Cosa Nostra organized-crime family — I was aware of La Cosa Nostra culture at an early age. I know or knew of many of the people in this book.

I was in my late 20s and early 30s living in South Philly during Scarfo’s reign, and I recall vividly the mob war and the many murders that occurred in South Philadelphia and Atlantic City. I’ve also interviewed Philadelphia cops and FBI agents from that era, and I found Leonetti’s descriptions of events, people and places to be frank and accurate.

I spoke recently to Philip Leonetti, who called me from an undisclosed location, as his uncle has placed a $500,000 contract on his life. Leonetti told me he wrote the book because, first, it is a great story. Second, he wrote the book so his son will understand his life in organized crime and how he was schooled in La Cosa Nostra from an early age by his uncle.

“From when I was little he would tell me we don’t talk about our life to anybody,” Leonetti told me. “We’re different; we don’t live by the same rules like everybody else. If somebody bothers us, we’ll kill the guy ourselves. We don’t rat to the police. This is the environment I grew up in.”

He described his uncle as smart, devious, calculating and psychopathic. Leonetti admitted to committing murders and said he tried to be a good soldier for his uncle by killing — and he was good at it — but he didn’t enjoy the act like his uncle did.

“All the crimes I committed, like the murders I was involved in, were all against bad people, guys that were involved in our life, so I didn’t think anything of it,” Leonetti explained. “They were looking to kill us, and we were looking to kill them. We weren’t looking to kill no legitimate people.”

Leonetti said he is happy in his new straight life, and he wishes he had lived this way all his life. He said he did not miss the treachery and killing from his past life in La Cosa Nostra, but he admitted, “I miss the money.”

“Mafia Prince” offers an insider’s history of the dark, violent world of La Cosa Nostra.

• Paul Davis is a writer who covers crime, espionage and terrorism. He can be reached at [email protected]